C/EBPα Regulates Human Adiponectin Gene Transcription Through an Intronic Enhancer

  1. Liping Qiao1,
  2. Paul S. MacLean2,
  3. Jerome Schaack3,
  4. David J. Orlicky4,
  5. Christian Darimont5,
  6. Michael Pagliassotti6,
  7. Jacob E. Friedman78 and
  8. Jianhua Shao1
  1. 1Graduate Center for Nutritional Sciences, University of Kentucky, Lexington, Kentucky
  2. 2Department of Medicine, University of Colorado Health Sciences Center, Denver, Colorado
  3. 3Department of Microbiology, University of Colorado Health Sciences Center, Denver, Colorado
  4. 4Department of Pathology, University of Colorado Health Sciences Center, Denver, Colorado
  5. 5Nestle Research Center, Lausanne, Switzerland
  6. 6Department of Food Science & Human Nutrition, Colorado State University, Fort Collins, Colorado
  7. 7Department of Pediatrics, University of Colorado Health Sciences Center, Denver, Colorado
  8. 8Department of Biochemistry & Molecular Genetics, University of Colorado Health Sciences Center, Denver, Colorado
  1. Address correspondence and reprint requests to Jianhua Shao, MD, PhD, Graduate Center for Nutritional Sciences, University of Kentucky, 900 S. Limestone, Lexington, KY 40536. E-mail: jianhuashao{at}uky.edu

Abstract

Adiponectin is an adipose-derived hormone that enhances insulin sensitivity and plays an important role in regulating energy homeostasis. Here, we demonstrate that the DNA encoding the first intron of the human adiponectin gene contains an intronic enhancer that regulates adiponectin gene expression in an adipose tissue–specific manner. Insertion of the DNA encoding the first intron into reporter constructs containing the proximal adiponectin promoter (Pro-Int1-Luc) resulted in a 20-fold increase in activity relative to the promoter alone in 3T3-L1 adipocytes. Coexpression of CCAAT/enhancer-binding protein (C/EBP)α increased luciferase activity of the Pro-Int1-Luc construct ∼75-fold but had no effect on the constructs containing the proximal adiponectin promoter alone. At least eight potential C/EBPα response elements are located between +3000 to +10000 nucleotides within the DNA encoding the first intron, including a 34-bp core sequence for the intronic enhancer that contains three tandem C/EBPα response elements. However, the intronic enhancer is not conserved between human and mouse. Overexpression or siRNA-mediated knockdown of endogenous C/EBPα significantly increased or decreased, respectively, adiponectin mRNA levels in differentiated human Chub-S7 adipocytes, while neither C/EBPβ nor C/EBPδ significantly affected adiponectin expression in mature adipocytes. Thus, C/EBPα is a key transcription factor for full activation of human adiponectin gene transcription in mature adipocytes through interaction with response elements in the intronic enhancer.

Footnotes

  • The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

    • Accepted March 16, 2005.
    • Received October 11, 2004.
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